Fall Protection in Space

The European Space Agency landed their Philae probe on a comet named 67P on Wednesday, November 12. It’s sort of a big deal. Philae only had 60 hours of battery life once it was game time, so obviously the first thing it did was take a selfie, because #TechnologyAndStuff:

(Okay, here’s the real selfie.) It’s really only a matter of time before comet tourism becomes a thing, which means we’ll have to have the infrastructure to support it. Luckily for work-at-height professionals, that means job security for a long time erecting cell towers in space. The moon will probably be the first place we start building cell towers, but after that 67P will definitely get one and maybe Jupiter after that. Maybe the forest moon of Endor after that. There’s one wrinkle in our plans that we need to address, however: fall protection. There’s a very good chance* that your gear was only designed to work on Earth, so we decided to do some calculations using a standard 6′ lanyard with a factor 1 and factor 2 fall. Let’s start of with some assumptions we’re making: you weigh 100 kg, and since you’ll be in hazardous space conditions you’ll also be donning a 91 kg space suit. Thanks to Isaac Newton and drop test results from Miller, here’s what you can expect in various planetary conditions.

Earth

If you fell 6′ on Earth (a factor 1 fall), you would achieve a velocity of 5.94 m/s (13 mph) by the time your lanyard caught you. If your lanyard doesn’t have any shock absorption, you would experience 4,000 lbf. If it does have a shock pack, you’d only experience 794 lbf. If, on the other hand, you fell 12′ (a factor 2 fall), you would achieve a velocity of 8.4 m/s (19 mph) before your lanyard caught you. Again, without shock absorption we’re talking 7,900 lbf. Yikes. You can drop that down to 2,300 lbf with a standard shock pack.

The Moon

Though a comet has more wow factor right now, let’s face the facts: the most likely interstellar body you’ll be building cell towers on after Earth is the moon, which has only 16% of the gravity of Earth. A factor 1 fall on the moon is not nearly as bad as Earth, because you’ll only be going 2.4 m/s (5 mph) by the time your lanyard catches you. Without shock absorption, that’s 1,300 lbf. With it, you’d only feel 250 lbf. No biggie. A factor 2 fall is a little more serious: you’d be going 3.4 m/s (8 mph) and you’d experience approximately 2,500 lbf (or 716 lbf with a shock pack).

Jupiter

Okay, so far so good. You’d actually be a little bit safer on the moon from fall-related injuries. But let’s look at a scenario that’s worse than Earth. How about Jupiter, which has 2.5x the gravitational force of Earth? Yeah, okay. You’re right; we can’t technically build cell towers on planets made entirely out of gas. Fair enough. Humor me. After falling 6 feet on Jupiter you’d be zipping along at 9.5 m/s (21 mph). Without shock absorption, we’re talking 19,000 lbf. With a shock pack we could drop that down to 3,800 lbf, but you’re still probably going to be seriously injured or killed by something like that. Clearly we can see that if you’re not likely to survive a 6′ fall, a 12′ fall won’t offer much more hope. Anyhow, if you were to fall 12′ on Jupiter, you would be going 13.4 m/s (30 mph). For perspective, you’d be accelerating 1.5x faster than a formula 1 race car. Zero to 60 in 1 second. Without a shock pack, that would be a massive 38,000 lbf (which is almost double the force of a car crash at 60 mph). With a standard shock pack, you’d still hit approximately 11,000 lbf. Ouch. We’ll have to go without cell service on Jupiter until we can find another way.

The Comet 67P

If your boss sends you out on a job on the next flight to 67P, don’t worry too much about fall protection. It only has about 1/10,000 the gravity of Earth, and so with a factor 2 fall you’d only generate about 2 lbf. That’s about as gentle as getting touched by someone. But that leaves the opposite hazard of accidentally floating out into space. So don’t do that.

Conclusion

In order to facilitate more intergalactic selfies (which is so necessary for the flourishing of society), we’ll definitely be building cell towers on other planets in the foreseeable future. Our recommendation is that fall protection manufacturers start designing equipment that can handle increased gravity. *About a 100% chance, ± 0%.

Bonus: Calculate Your Own Fall Force!

Enter your weight and then select a planet to calculate your own unique fall force.
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